The effect of regional tectonic setting on local fault response to magmatic activity
Abstract
There is substantial evidence for mechanical coupling between crustal faults and magmatic systems. Large earthquakes release accumulated stress onto a nearby magmatic system, triggering an eruption. Conversely, processes leading to physical changes in a magmatic system (e.g., injection or withdrawal of magma) may load stresses onto nearby faults, triggering earthquakes. Although the triggering mechanisms for these phenomena are not yet fully understood, it is clear that crustal faults in volcanic regions may receive and respond to stresses from both tectonic and magmatic processes. Thus, it is critical to examine how the interaction of tectonically- and magmatically-generated stress fields affects faults in the Earth's crust, in order to accurately interpret earthquake data from volcanic regions and to refine assessments of earthquake and eruption likelihood. In this study, we examine this interaction by calculating Coulomb stress changes on local faults induced by a specified dike inflation event in a background stress field of systematically varying magnitude and orientation. We find that patterns of seismicity (earthquake locations and fault-plane solutions) resulting from dike inflation depend strongly on the relative strength and orientation of background tectonic stresses. In an isotropic tectonic stress field inflation-induced stresses dominate local fault behavior, and strike-slip faulting with a `reversed' sense of slip (fault-plane solution p-axis orientation ~90° to dike orientation/regional σ1) is expected in a large region surrounding the inflating dike. In a strongly deviatoric tectonic stress field, faults in the walls of the dike lock and no fault slip whatsoever is expected in this region. However, faulting with a `regional' sense of slip (p-axis orientation parallel to dike orientation/regional σ1) is encouraged in zones extending from the tips of the inflating dike (forming a dogbone pattern of epicenters). Patterns of earthquake activity similar to those predicted by Coulomb stress modeling have been observed at several recently active volcanoes, and appear to correspond to the relative strength of the regional stress field. Thus, it is critical to consider the regional tectonic setting when interpreting patterns of volcanotectonic seismicity in terms of magmatic processes. Ultimately, the interactions between tectonic setting, other local stresses, and magma ascent are complex and will vary from eruption to eruption, even at a single volcano. However, careful consideration of the relative importance of these factors may elucidate physical processes occurring within the magmatic system and may provide a basis for refined forecasts of volcanic activity based on the characteristics of VT seismicity.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.V51G..02R
- Keywords:
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- 1217 Time variable gravity (7223;
- 7230);
- 1242 Seismic cycle related deformations (6924;
- 7209;
- 7223;
- 7230);
- 7280 Volcano seismology (8419);
- 8164 Stresses: crust and lithosphere;
- 8419 Volcano monitoring (7280)